1. Field of the Invention
The present invention generally relates to a ventilation system with controllable air input and output and, more particularly, to a ventilation system with controllable air input and output that is installed in a building to control ventilation of the building.
2. Description of the Related Art
Referring to FIG. 1, a conventional tube-type air intake and exhaust structure is shown. The air intake and exhaust structure comprises a ventilation system 9 having an inner tube 91 and an outer tube 92 coaxial with the inner tube 91. The inner tube 91 has an intake air channel 911, and an exhaust channel 921 is formed between the inner tube 91 and the outer tube 92. The inner tube 91 has an air-guiding cover 93 at one end thereof for collecting airflows.
The ventilation system 9 further comprises an extra outer tube 94 on a top of the outer tube 92. The outer tube 94 has a windward opening 941 and an air-guiding opening 942 lower than the windward opening 941. Based on the height difference between the windward opening 941 and the air-guiding opening 942, when the wind brings the air of the windward opening 941 to the air-guiding opening 942, the air from the windward opening 941 will cause the air of the air-guiding opening 942 to whirl. This will enhance an air-pulling effect at the air-guiding opening 942. The air-pulling effect will speed up the air circulation of the ventilation system 9, thereby providing better ventilation.
However, the ventilation system 9 is not equipped with any device that can stop its air circulation when it is desired. For example, when the ventilation system 9 is connected to architecture such as a factory or a tunnel where a fire accident takes place, the ventilation system 9 may instead cause the fire to spread quickly due to good air circulation provided thereby. In light of this problem, it is desired to improve the ventilation system 9.